clusterApply arguments

Thank you for your answer!
I agree with you except for the 3 (Error) example and
I realize now I should have started with that in the explanation.

From my point of view
parLapply(cl = clu, X = 1:2, fun = fun, c = 1)
shouldn't give an error.

This could be easily avoided by using all the argument
names in the custerApply call of parLapply which means changing,

parLapply <- function(cl = NULL, X, fun, ...)  {
    cl <- defaultCluster(cl)
    do.call(c, clusterApply(cl, x = splitList(X, length(cl)),
            fun = lapply, fun, ...), quote = TRUE)
}

to

parLapply <- function (cl = NULL, X, fun, ...)  {
    cl <- defaultCluster(cl)
    do.call(c, clusterApply(cl = cl, x = splitList(X, length(cl)),
            fun = lapply, fun, ...), quote = TRUE)
}

.

Best regards,
Florian



Gesendet: Mittwoch, 14. M?rz 2018 um 19:05 Uhr
Von: "Henrik Bengtsson" <henrik.bengtsson at gmail.com>
An: "Florian Schwendinger" <Florian_Schwendinger at gmx.at>
Cc: fschwend at wu.ac.at, R-devel <r-devel at r-project.org>
Betreff: Re: [Rd] clusterApply arguments
This is nothing specific to parallel::clusterApply() per se. It is the
default behavior of R where it allows for partial argument names. I
don't think there's much that can be done here except always using
fully named arguments to the "apply" function itself as you show.

You can "alert" yourself when there's a mistake by using:

options(warnPartialMatchArgs = TRUE)

e.g.

clusterApply(clu, x = 1:2, fun = fun, c = 1) ## Error

Warning in clusterApply(clu, x = 1:2, fun = fun, c = 1) :
partial argument match of 'c' to 'cl'
Error in checkCluster(cl) : not a valid cluster

It's still only a warning, but an informative one.

/Henrik

On Wed, Mar 14, 2018 at 8:50 AM, Florian Schwendinger
<Florian_Schwendinger at gmx.at> wrote:

Hi!

I recognized that the argument matching of clusterApply (and therefore parLapply) goes wrong when one of the arguments of the function is called "c". In this case, the argument "c" is used as cluster and the functions give the following error message "Error in checkCluster(cl) : not a valid cluster".

Of course, "c" is for many reasons an unfortunate argument name and this can be easily fixed by the user side.

See below for a small example.

library(parallel)

clu <- makeCluster(2, "PSOCK")

fun <- function(x0, x1) (x0 + x1)
clusterApply(clu, x = 1:2, fun = fun, x1 = 1) ## OK
parLapply(cl = clu, X = 1:2, fun = fun, x1 = 1) #OK


fun <- function(b, c) (b + c)
clusterApply(clu, x = 1:2, fun = fun, c = 1) ## Error
clusterApply(cl = clu, x = 1:2, fun = fun, c = 1) ## OK
parLapply(cl = clu, X = 1:2, fun = fun, c = 1) ## Error

stopCluster(clu)


I used "R version 3.4.3 Patched (2018-01-07 r74099".


Best regards,
Florian